Not so keen on using drywall or Denshield (which has a layer of drywall) in the shower even with topical coverage...just in case. Cement board seems the obvious and proven alternative with hydroban on top. I will have a vapour barrier behind the cement board. Should water get into the cement board it's not getting into the wall. Now the question is where will that water go if the bottom of the backerboard is sealed at the base / at the junction to the shower acrylic base? Looks like it will run down the backer board and collect at the bottom with no place to drain to.

Would it make sense to just not seal the bottom of the backerboard with hydroban , nor silicone the gap between the tile and the shower pan so that water candrain into the shower pan?